Structure and control of negative thermal expansion of Nd/Sm substituted 0.5PbTiO3–0.5BiFeO3 ferroelectrics

Controlling negative thermal expansion (NTE) has always been an important but difficult issue for the study of NTE materials and their future applications. It is well known that the ferroelectric material 0.5PbTiO3–0.5BiFeO3 exhibits a strong negative thermal expansion behavior in the tetragonal phase. In this work, Nd/Sm substitution in the ferroelectric material 0.5PbTiO3–0.5BiFeO3 has been studied specifically to control the NTE. The NTE is much weakened in 0.5PbTiO3–0.5Bi0.8Nd0.2FeO3 and 0.5PbTiO3–0.5Bi0.8Sm0.2FeO3 compared with the parent 0.5PbTiO3–0.5BiFeO3. The relationship between spontaneous volume ferroelectrostriction (SVFS) and ferroelectricity is studied, and the result indicates that the SVFS shows a strong correlation with the square of spontaneous polarization (PS) displacement (δzA2). The present study shows that control of the NTE of PT-based ferroelectric materials can be achieved by the adjustment of ferroelectricity.